The IMS is an all Internet protocol (ALL-IP)-based core network for combining wired and wireless environments, and is an infrastructure for providing multimedia services. The IMS was first proposed by the 3rd Generation Partnership Project (3GPP) group for developing international standards for radio communication.
The major motive for using the All-IP-based network through the IMS is to combine many contents and new service performance through a packet service. That is, the basic service target desired by the IMS is to provide multimedia such as voice, audio, video, and data in a complex manner based on the IP protocol, and also to build an infrastructure allowing quick service development and modification.
In order to provide the IMS service, a session is established after performing a negotiation process for transmitting and receiving capabilities or preferences between end users. After the session is established, a bearer is formed between the end users' terminals to thus allow data communication.
The IMS uses the SIP protocol provided by the Internet engineering task force (IETF) so as to establish the above-noted session.
The SIP is an application-level signaling protocol that has specified the process for intelligent terminals attempting to communicate on the Internet to identify each other, find their positions, and generate, delete, or modify multimedia communication sessions between them.
In the SIP-based communication, a call sending person transmits and receives text messages to/from a call receiving person, and the actual contents of the established session are described while including at least one of media formats such as the audio, video, and text in the message.
In this instance, the session is established in correspondence to the service. That is, a session is established between the call sending person and the call receiving person so as to provide a specific service. When attempting to change negotiation information of the session because of addition of media, the established session negotiation is performed again through a re-INVITE message for the existing session.
However, the re-negotiation process for the session is very complicated. For example, when a receiving person who has requested to re-negotiate the session cannot accept a newly defined media format, the receiving person notifies the call sending person of the fact that he cannot accept the re-negotiation-requested media format, and he performs a complex process for negotiating the session according to the media format available for both persons.
Accordingly, it is restricted to change the detailed contents of the service when the session is once connected in a like manner of adding various media formats during participation in a session.
For example, it is not easy to add video media to 3 persons from among 5 persons who are participating in a chatting service session since the media format of the negotiated chatting service session must be changed.
Also, when a person from among those who are requested to re-negotiate an addition of the video media rejects the addition of the media, the existing chatting service session may be terminated or another negotiation may be required.
Further, when the person participates in the video service session, terminates the video service, and then attempts to switch to the chatting service, it is burdensome because he must perform a re-negotiation process for defining the media format of the session.
In addition, when a problem occurs during the session re-negotiation process, the existing service he is joining and a new service he desires to join may generate problems.
However, when considering that the characteristic of the IMS service is to combinatively provide various multimedia having different media formats, a service is configured with various media formats, and hence, the session will be frequently re-negotiated while the session is connected.
Therefore, since the conventional session negotiation method limits provision of complex multimedia services configured with various media formats, it is needed to provide a session processing scheme appropriate for the characteristic of the IMS service that has minimized the limit.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.